Method For Polishing an Optical Surface By Means of a Polishing Tool

ABSTRACT

Polishing method comprising a step of receiving a surface to be polished, a configuration step during which the polishing machine is configured, and a polishing step during which the optical surface is polished, wherein the angle of inclination of the pin is between 2° and 20°, the inner cusp point is between −10 mm and 10 mm, the outer cusp point is between R−15 mm and R−5 mm, the speed of advance is between 100 mm/min and 2000 mm/min; the speed of rotation is between 500 rpm and 3000 rpm; and the bearing force is between 50 N and 180 N.

RELATED APPLICATIONS

This application is a U.S. National Phase Application under 35 USC 371 of International Application PCT/EP2013/054493 filed Mar. 6, 2013.

This application claims the priority of French application No. 1252060 filed Mar. 7, 2012, the entire content of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a method for polishing an optical surface by means of a polishing tool, as well as to a method for surfacing a surface, to a computer program product comprising a series of instructions which, when loaded on a computer, leads to the steps of the methods according to the invention being carried out, and to a polishing machine.

BACKGROUND OF THE INVENTION

Conventionally, the optical surface of an optical lens, in particular an ophthalmic lens, is obtained by means of a surfacing method comprising a machining step followed by a step of polishing the machined surface.

The machining step consists in machining the surface of the optical lens with a machining tool in order to impart the desired thickness and radii of curvature to the lens.

At the end of the machining step, the lens has the curvatures and thickness corresponding to the desired optical function, but the machined surface of the lens is depolished.

During the polishing step, the machined surface of the lens is polished by means of a polishing tool. The polishing step is intended to eliminate all marks left on the surface of the lens by the machining.

At the end of the polishing step, the lens is smooth and transparent and capable of fulfilling the optical function for which it was designed.

Often, an ophthalmic lens polishing centre requires several varieties of polishing tool (more or less curved and/or of variable diameter) in order to be able to process all the lenses which may be encountered.

Furthermore, the parameters of the polishing method vary depending on the type of lens to be polished. For example, for a given polishing tool and a given surface, it is suitable to set the angle of inclination, the inner cusp point, the outer cusp point, the speed of advance of the tool, the speed of rotation of the lens to be polished, and the bearing force of the polishing tool on the surface to be polished.

Among the parameters of lenses which can have an influence on the choice of the polishing tool and the parameters of the polishing machine, the following may be mentioned: the base, the cylinder, the diameter, the material, the addition and the design, for example in the case of a progressive lens the progression length and the inset of the near vision.

Finally, the choice of the polishing tool and of the parameters of the polishing method may depend on the operator, who might make a choice which turns out not to be optimal. In particular, depending on the tool selected and the parameters adopted, the polishing time may vary greatly from one lens to another. Thus, some lenses risk being insufficiently or poorly polished whereas, for other lenses, the polishing time will be longer than the time necessary.

SUMMARY OF THE INVENTION

One object of the invention is to provide a polishing method which is simple to carry out and which permits a compromise between the duration of the polishing method, compliance with the shape of the surface to be polished and a sufficient level of polishing so as not to impair the wearer's vision.

To this end, one aspect of the invention is directed to a method for polishing an optical surface by means of a polishing tool, the polishing method comprising:

-   -   a step of receiving a surface, during which an optical surface         to be polished is received,     -   a configuration step, during which the polishing machine         comprising a polishing tool is configured,     -   a polishing step, during which the optical surface is polished         by means of the polishing machine configured during the         configuration step,     -   wherein:         -   during the configuration step, the polishing machine is             configured in such a way that:             -   the angle of inclination of the pin is greater than or                 equal to 2° and less than or equal to 20°,             -   the inner cusp point is greater than or equal to −10 mm                 and less than or equal to 10 mm,             -   the outer cusp point is greater than or equal to R−15 mm                 and less than or equal to R−5 mm, with R being the                 half-diameter of the circle circumscribed on the surface                 to be polished, expressed in millimetres;             -   the speed of advance is greater than or equal to 100                 mm/min and less than or equal to 2000 mm/min;             -   the speed of rotation of the surface to be polished is                 greater than or equal to 500 rpm and less than or equal                 to 3000 rpm; and             -   the bearing force is greater than or equal to 50 N and                 less than or equal to 180 N.

Advantageously, the method according to an embodiment of the invention makes it possible to set the parameters of the polishing machine independently of the lens to be polished, and to obtain a good compromise between the duration of the polishing method, compliance with the shape of the surface to be polished and a sufficient level of polishing so as not to impair the wearer's vision.

Surprisingly, the Inventors have been able to observe that, when the parameters of the polishing machine are selected in the value ranges according to the invention, it is possible to polish lenses comprising a rear face having a base, expressed in terms of an index of 1.53, of between −12 and −0.25 dioptres and a cylinder ranging up to 4 dioptres for a lens having an index of 1.53. These lenses represent about 80% of the ophthalmic lenses manufactured.

Thus, by applying the method according to the invention, at least 80% of ophthalmic lenses can be polished effectively.

Furthermore, the method according to the invention makes it possible to polish ophthalmic lenses by using a single type of polishing tool. Thus, when carrying out a method according to the invention, it is not necessary to have several varieties of polishing tool.

A method for polishing an optical surface according to an embodiment of the invention may furthermore comprise one or more of the optional characteristics below, considered individually and/or according to all possible combinations:

-   -   the polishing step has a duration greater than or equal to 20         seconds and less than or equal to 130 seconds;     -   the polishing step has a duration independent of the surface         properties and the material of the optical surface to be         polished, the duration of the said polishing step being greater         than or equal to 60 seconds and less than or equal to 80         seconds;     -   the polishing tool comprises:         -   a rigid support having a transversal end surface and             belonging to a base having a flexible flange surrounding the             support;         -   an elastically compressible interface which is applied             against and covers the end surface of the flexible flange             located on the same side as the said end surface;         -   a flexible pad which is adapted to be applied against the             optical surface and which is applied against and at least             partly covers the interface opposite and in line with the             said end surface, the pad having a so-called central part             which lies in line with the said end surface and a so-called             peripheral part which lies transversely beyond the end             surface; and         -   elastic returning means connecting the peripheral part to             the support,             the combination of the said peripheral part and the             returning means forming a means for stabilization of the             tool during the polishing;     -   the angle of inclination of the pin is greater than or equal to         5°;     -   the angle of inclination of the pin is less than or equal to         15°;     -   the angle of inclination of the pin is greater than or equal to         5° and less than or equal to 15°;     -   the inner cusp point is non-zero;     -   the inner cusp point is greater than or equal to −5 mm;     -   the inner cusp point is less than or equal to 5 mm;     -   the inner cusp point is non-zero and greater than or equal to −5         mm and less than or equal to 5 mm;     -   the outer cusp point is greater than or equal to R−12 mm;     -   the outer cusp point is less than or equal to R−8 mm;     -   the outer cusp point is greater than or equal to R−12 mm and         less than or equal to R−8 mm;     -   the speed of advance is greater than or equal to 500 mm/min;     -   the speed of advance is greater than or equal to 750 mm/min;     -   the speed of advance is less than or equal to 1500 mm/min;     -   the speed of advance is greater than or equal to 750 mm/min and         less than or equal to 1500 mm/min;     -   the speed of rotation of the surface to be polished is greater         than or equal to 900 rpm;     -   the speed of rotation of the surface to be polished is less than         or equal to 2100 rpm;     -   the speed of rotation of the surface to be polished is greater         than or equal to 900 rpm and less than or equal to 2100 rpm;     -   the bearing force of the polishing tool on the lens is greater         than or equal to 80 N;     -   the bearing force of the polishing tool on the lens is less than         or equal to 150 N;     -   the bearing force of the polishing tool on the lens is greater         than or equal to 80 N and less than or equal to 150 N.

Another aspect of the invention relates to a method for surfacing an optical surface, comprising:

-   -   a data reception step, during which surface data defining the         optical properties of a surface are received,     -   a step of machining the optical surface, during which the         optical surface is machined as a function of the surface data,     -   a polishing step, during which the machined surface is polished         by means of a polishing method according to an embodiment of the         invention.

Another aspect of the invention relates to a computer program product comprising a series of instructions which, when loaded in a computer, leads to the said computer or a polishing machine, for example, carrying out the steps of a method according to an embodiment of the invention.

Another aspect of the invention relates to a polishing machine configured for carrying out the steps of the polishing method according to an embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be understood more clearly on reading the following description, given solely by way of example and provided with reference to the appended drawings, in which:

FIG. 1 illustrates the steps of the processing method according to the an embodiment of the invention,

FIG. 2 illustrates the angle of inclination of the pin, and

FIGS. 3 and 4 illustrate the inner and outer cusp points.

DETAILED DESCRIPTION OF THE DRAWINGS

For reasons of clarity, the various elements represented in the figures are not necessarily to scale.

As represented in FIG. 1, the method according to the invention for polishing an optical surface by means of a polishing tool comprises:

-   -   a step S1 of receiving a surface,     -   a configuration step S2, and     -   a polishing step S3.

During the step S1 of receiving a surface, the optical surface to be polished is received. For example, a lens, at least one of the faces of which has been machined, is received.

According to one embodiment of the invention, the lens received comprises a rear face having a base, expressed in terms of an index of 1.53, of between −12 and −0.25 dioptres and a cylinder ranging up to 4 dioptres. Some received lenses may have a locally convex rear face.

The optical lens may be made of various organic materials, for example polycarbonate, or of poly(diethylene glycol bis(allyl carbonate)) having an optical index of 1.498, known by the brand name CR39, or a thermosetting polymer having an optical index of 1.665, known by the brand name MR7.

Following the reception of the surface to be polished, the polishing machine comprising the polishing tool is configured during the configuration step S2.

During the configuration step S2, the configuration parameters of the polishing machine are selected in predetermined value ranges.

The angle of inclination a of the pin b of the polishing tool is greater than or equal to 2°, for example greater than or equal to 5°, and less than or equal to 20°, for example less than or equal to 15°.

As represented in FIG. 2, the angle of inclination a of the pin b is defined as being the angle between the rotation axis of the lens L and the straight line normal to the chord joining the centre of rotation of the lens to the highest point on the contour of the lens.

According to one embodiment of the invention, the value of the angle of inclination of the pin may be selected discretely from the values 5°, 10° or 15°.

As represented in FIGS. 3 and 4, during the polishing step the polishing tool p will execute a continuous sweeping movement, without stopping, over the surface of the lens L. Depending on the variants of the polishing method, the sweeping movement of the tool over the surface of the lens may be obtained either by movement of the polishing tool p or by movement of the lens to be polished, or by a combination of relative movements between the polishing tool p and the lens L.

As represented in FIG. 3, the inner cusp point corresponds to the point where the pin makes a U-turn in its translational movement before moving back towards the edge of the lens.

According to one embodiment of the invention, the inner cusp point lies at a distance less than or equal to 10 mm, for example less than or equal to 5 mm, from the centre of the circle circumscribed on the surface to be polished.

According to one embodiment, the inner cusp point is different from the centre of the circle circumscribed on the surface to be polished.

As illustrated in FIG. 3, the outer cusp point corresponds to the point where the pin makes a U-turn in its translational movement before moving back towards the centre of the lens.

According to one embodiment of the invention, the outer cusp point lies at a distance greater than or equal to R−15 mm, for example greater than or equal to R−12 mm, and less than or equal to R−5 mm, for example R−8 mm, from the centre of the circle circumscribed on the surface to be polished, with R being the half-diameter of the circle circumscribed on the surface to be polished.

The speed of advance of the polishing tool in translation is greater than or equal to 100 mm/min, for example greater than or equal to 500 mm/min, for example even greater than or equal to 750 mm/min, and less than or equal to 2000 mm/min, for example 1500 mm/min.

The speed of rotation of the lens to be polished is greater than or equal to 500 rpm, for example 900 rpm, and less than or equal to 3000 rpm, for example less than or equal to 2100 rpm.

The bearing force exerted by the pin which presses the polishing tool to match the surface to be polished is greater than or equal to 50 N, for example greater than or equal to 80 N, and less than or equal to 180 N, for example less than or equal to 150 N.

According to one embodiment of the invention, the bearing force is selected to be greater than or equal to 100 N.

During the configuration step, the operator configures the parameters of the polishing machine in the ranges defined by the invention.

Advantageously, the use of the polishing machine with parameters according to the invention makes it possible to obtain a surface both fulfilling the optical function of the lens, and ensuring a sufficient level of polishing so as not to impair the wearer's vision, in a polishing time greater than or equal to 20 s and less than or equal to 130 s.

During the polishing step S3, the optical surface is polished by means of the polishing machine configured during the configuration step.

According to one embodiment of the invention, the polishing step has a duration independent of the surface properties and the material of the optical surface to be polished. The polishing step may have a duration greater than or equal to 60 s and less than or equal to 80 s.

According to one embodiment of the invention, the method according to the invention may comprise a step of supplying the polishing tool, during which the polishing tool is supplied.

According to one embodiment of the invention, during the step of supplying the polishing tool, the tool supplied comprises:

-   -   a rigid support having a transversal end surface and belonging         to a base having a flexible flange surrounding the support;     -   an elastically compressible interface which is applied against         and covers the end surface of the flexible flange located on the         same side as the said end surface;     -   a flexible pad which is adapted to be applied against the         optical surface and which is applied against and at least partly         covers the interface opposite and in line with the said end         surface, the pad having a so-called central part which lies in         line with the said end surface and a so-called peripheral part         which lies transversely beyond the end surface; and     -   elastic returning means connecting the peripheral part to the         support,         the combination of the said peripheral part and the returning         means forming a means for stabilization of the tool during the         polishing.

According to one embodiment of the invention, the polishing tool may be a tool as described in WO2007/128894.

The polishing tool may have an overall diameter greater than or equal to 50 mm, for example greater than or equal to 55 mm, and less than or equal to 70 mm, for example less than or equal to 60 mm.

According to one embodiment of the invention, the diameter of the transversal end surface of the rigid support is greater than or equal to 20 mm, for example greater than or equal to 29 mm, and less than or equal to 40 mm, for example less than or equal to 31 mm. According to one embodiment, the diameter of the transversal end surface of the rigid support is substantially equal to 30

MM.

The transversal end surface of the rigid support may have a radius of curvature greater than or equal to 70 mm and less than or equal to 200 mm.

According to one embodiment of the invention, the elastically compressible interface has a thickness greater than or equal to 6 mm, for example greater than or equal to 8 mm, and less than or equal to 12 mm, for example less than or equal to 10 mm. The thickness of the elastically compressible interface may be substantially equal to 9 mm.

A plurality of different materials may be used for the elastically compressible interface. Among the materials which can be used, the polyurethane foam known by the brand name Sylomer may be mentioned. This is a polyurethane foam having a density of between 150 kg/m³ and 1000 kg/m³, withstanding a high allowable load ranging up to 2105 N/m², and a compression of up to 40% of its thickness.

According to one embodiment, the flexible pad has a thickness greater than or equal to 0.8 mm and less than or equal to 1.2 mm. The flexible pad may have a Shore A hardness greater than or equal to 50, for example greater than or equal to 60, and less than or equal to 80, for example less than or equal to 70.

Preferably, the material constituting the flexible pad is porous in order to allow liquid abrasive to pass through and to remove the material eroded during the polishing step.

According to one embodiment of the invention, the abrasive is aluminium oxide (alumina Al₂O₃) having a median dimension (D50) of between 1 and 2.5 μm, in suspension in a liquid in a ratio of about 200 g of abrasive per litre of liquid.

The polishing method according to the invention may be carried out by means of polishing machines known to the person skilled in the art.

For example, the machine described in US 2009/0011688 may be used for carrying out a method according to the invention.

It is to be understood that the invention may be reproduced in forms other than those of the embodiments which have been described in detail.

The invention is not limited to the embodiments described, which should be interpreted nonlimitingly and as including all equivalent versions. 

1. A method for polishing an optical surface by means of a polishing tool, the polishing method comprising: a step of receiving a surface, during which an optical surface to be polished is received; a configuration step, during which the polishing machine comprising a polishing tool is configured; and a polishing step, during which the optical surface is polished by means of the polishing machine configured during the configuration step, wherein during the configuration step, the polishing machine is configured in such a way that: the angle of inclination (α) of the pin is greater than or equal to 2° and less than or equal to 20°, the inner cusp point is greater than or equal to −10 mm and less than or equal to 10 mm, the outer cusp point is greater than or equal to R−15 mm and less than or equal to R−5 mm, with R being the half-diameter of the circle circumscribed on the surface to be polished, expressed in millimetres; the speed of advance is greater than or equal to 100 mm/min and less than or equal to 2000 mm/min; the speed of rotation of the surface to be polished is greater than or equal to 500 rpm and less than or equal to 3000 rpm; and the bearing force is greater than or equal to 50 N and less than or equal to 180 N.
 2. The method according to claim 1, wherein the polishing step has a duration greater than or equal to 20 seconds and less than or equal to 130 seconds.
 3. The method according to claim 1, wherein the polishing step has a duration independent of the surface properties and the material of the optical surface to be polished, the duration of said polishing step being greater than or equal to 60 seconds and less than or equal to 80 seconds.
 4. The method according to claim 1, wherein the polishing tool comprises: a rigid support having a transversal end surface and belonging to a base having a flexible flange surrounding the support; an elastically compressible interface which is applied against and covers the end surface of the flexible flange located on the same side as said end surface; a flexible pad which is adapted to be applied against the optical surface and which is applied against and at least partly covers the interface opposite and in line with said end surface, the pad having a so-called central part which lies in line with said end surface and a so-called peripheral part which lies transversely beyond the end surface; and elastic returning means connecting the peripheral part to the support, the combination of the peripheral part and the returning means forming a means for stabilization of the tool during the polishing.
 5. The method according to claim 1, wherein the angle of inclination of the pin is greater than or equal to 5° and less than or equal to 15°.
 6. The method according to claim 1, wherein the inner cusp point is non-zero and greater than or equal to −5 mm and less than or equal to 5 mm.
 7. The method according to claim 1, wherein the outer cusp point is greater than or equal to R−12 mm and less than or equal to R−8 mm.
 8. The method according to claim 1, wherein the speed of advance is greater than or equal to 500 mm/min and less than or equal to 1500 mm/min.
 9. The method according to claim 1, wherein the speed of rotation is greater than or equal to 900 rpm and less than or equal to 2100 rpm.
 10. The method according to claim 1, wherein the bearing force is greater than or equal to 80 N and less than or equal to 150 N.
 11. A method for surfacing an optical surface, comprising: a data reception step, during which surface data defining the optical properties of a surface are received, a step of machining the optical surface, during which the optical surface is machined as a function of the surface data, and a polishing step, during which the machined surface is polished by means of a polishing method according to claim
 1. 12. A computer program product comprising a series of instructions which, when loaded in a computer, leads to the computer carrying out the steps of the method according to claim
 1. 13. A polishing machine configured for carrying out the steps of the method according to claim
 1. 